Extreme Value Analysis of Ocean Still Water Levels along the USA East Coast—Case Study (Key West, Florida)

Abstract

This paper provides an Extreme Value Analysis (EVA) of the hourly still water level (SWL) record at Key West, Florida dating back to 1913 to understand the statistical likelihood of the combination of high predicted tides and the more dynamic influences (predominantly hurricane induced storm surges) that can drive ocean water levels higher at the coast. The impact of hurricane ‘Wilma’ in 2005 dominates the records, producing a super-elevation of the SWL above Mean Sea Level (MSL) of 1155 mm with an estimated return period of around 147 years. This paper explores the duality of increasing risks of oceanic inundation due to extreme events and increasing mean sea level over time, whilst also providing a range of recommendations for ensuring improved predictive model fitting and robustness of EVA for SWLs measured at tide gauges. When integrated with future IPCC AR6 sea level projections, the return level plots from the EVA provide decision makers with key guidance for design, strategic planning and climate change adaptation purposes at Key West, Florida.

Extreme Value Analysis of Tide Gauge Record at the Port of Busan, South Korea

“…The study involved a range of methodologies and data sources explained in the following sub-sections. The methodology is in accord with the recommendations for the EVA of tide gauge data presented in Arns et al (2013) [17], augmented with some recent refinements that were advanced in Watson (2023) [19].…”

“…The EVA procedure applied to estimate extreme recurrence interval ocean water levels at Busan, South Korea, followed the general methodology presented in Watson (2023) [19], which are summarized in the following sub-sections. Importantly, the EVA is underpinned by input data that must conform to the statistical principles of independence and stationarity [15,[25][26][27][28][29].…”

“…Tide gauge records include all physical oceanographic processes as well as the longer-term trend elements associated principally with climate change (global sea level rise) and vertical land motion [9,30]. Determining and removing the trend from tide gauge records are not a straightforward undertaking [19], but an important aspect that can influence the utility of the EVA procedure [17].…”

“…The recommendations of Watson (2023) [19] were also applied, by using additional visual diagnostic outputs (e.g., Q-Q plots and recurrence interval plots) to confirm the model fit robustness of the more extreme observations within uncertainty bounds.…”

“…Although tide gauge observations confirm the primary driver for increasing ESWLs is the relative rise in the MSL over time, changes to trends in other ESWL contributory processes, such as surges and tides, have been noted in a range of key studies [11][12][13][14]. The EVA uses a Peaks Over Threshold (POT) approach with the selected peaks being fitted to a Generalized Pareto Distribution (GPD) in accordance with the best practice guidance from the literature (e.g., [15][16][17][18][19]) for application to tidal records. The 'extRemes' (version 2.0) extension package in R (version 4.3.2) [20,21] permits the automation of key analytical procedures.…”